The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventors hereof, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
The present disclosure relates generally to communications or storage systems and methods, and more particularly, to systems and methods for encoding and decoding for communications or storage systems utilizing coded modulation.
To improve the reliability of communications and storage systems, error control coding is commonly applied to the data that is conveyed or stored. A suitable error correcting code (ECC) can be applied to the data, which adds redundancy to the data stream. If the same throughput of data or storage space is desired in communication/storage, bandwidth expansion is often necessary. Bandwidth expansion refers to an increase in channel bandwidth, typically to allow transmission or storage to occur through the channel with a reduced symbol period or increased storage density. For some channels, especially for those that are low in quality, bandwidth expansion may not be possible or may not be desirable. In these situations, rather than increasing the needed bandwidth, the communication or storage system can utilize modulation schemes with a greater number of signal constellation points. For communications systems, this technique allows for more data to be transmitted at any given time. For example, signaling schemes that double the number of signal constellation points used for transmission, which therefore doubles the amount of data transmitted each symbol period, may produce substantially the same throughput as a signaling scheme that maintains the modulation scheme and doubles the channel bandwidth.
To fully utilize the advantages provided by increasing the number of signal constellation points, the type of modulation and the type of error correcting code should be designed to operate effectively together. This type of data encoding is typically referred to as coded modulation. When a convolutional code is used or the error correcting code, the system implements trellis coded modulation (TCM).
As described above, trellis coded modulation combines coding and modulation to achieve high data rates with little or no signal bandwidth expansion. However, a TCM scheme may leave behind residual errors that may negatively impact the performance of the communications or storage system.